"This narrow focus on Justice Souter's rulings on social issues has led to the claim that Mr. Obama is merely trading one liberal for another," Vitter wrote in a Washington Times op-ed.

"But there were other areas, such as those affecting free enterprise, where Justice Souter's decisions were much more constrained and deferential to government's two other branches, specifically relating to determinations that markets needed to be protected from overreaching liability, litigation risk or federal regulation," Vitter continued.

Vitter is one of the most socially conservative members of the Senate. His emphasis on free enterprise might signal the GOP hopes to avoid a polarizing confirmation hearing that focuses on abortion, an issue where Sotomayor has a slim record anyway.